A "color_map { ... }"
is a table of colors, which were assign to numbers between 0.00 an 1.00.
These color_maps we can use to colorate a variety of pattern.
The fastest way to understand this is by using the gradient pattern:

In a height of 1 unit this pattern is repeated.
If we want a smaller or an increased pattern, we can add after
(or before!) color_map a statement like "scale 0.25"
to "pigment".
In this way also turning ("rotate") and moving ("translate") is possible!

For a blue sky sphere with a diameter of 10000 units
and a color floating from white at the horizon to blue in zenit,
we need a sphere with the above color_map all together with "scale 10 000" --
Here we should put a "finish { ambient 1 diffuse 0}" because the sky is never shaded
by anything (I hope so!:-)